Apparatus for regulating the drive of a press or the like

ABSTRACT

The drive chains which are operative to intermittently move a series of gripper bars for conveying sheets through a printing press or the like each pass around a sprocket which is supported for movement in a direction aligned with the path of travel of the sheets. A pair of hydraulic pistons are provided for urging the sprockets for movement in a direction serving to maintain tension on the drive chains. When the gripper bars are stopped momentarily for seizing a sheet and for registering a sheet immediately prior to printing, cutting, or the like, excess chain movement is absorbed by the hydraulic pistons. A timing cam controls the operation of valves in the hydraulic system connected with the pistons, to regulate the supply of hydraulic fluid to the pistons in synchronism with the operation of the printing press.

United States Patent [191 Grutter Nov. 12, 1974 APPARATUS FOR REGULATING THE DRIVE OF A PRESS OR THE LIKE [75] Inventor: Walter Grutter,Morrens,

Switzerland [73] Assignee: J. Bobst & Fils, S.A., Switzerland [22] Filed: Mar. 12, 1973 [21] Appl. No.: 340,059

[30] Foreign Application Priority Data 3,718,250 2/1973 Bosworth 74/242.l4 R

Primary ExaminerLeonard H. Gerin Attorney, Agent, or Firm-Hill, Gross, Simpson, Van

Santen, Steadman, Chiara & Simpson [57] ABSTRACT The drive chains which are operative to intermittently move a series of gripper bars for conveying sheets through a printing press or the like each pass around a sprocket which is supported for movement in a direction aligned with the path of travel of the sheets. A pair of hydraulic pistons'are provided for urging the sprockets for movement in a direction serving to maintain tension on the drive chains. When the gripper bars are stopped momentarily for seizing a sheet and for registering a sheet immediately prior to printing, cutting, or the like, excess chain movement is absorbed by the hydraulic pistons. A timing cam controls the operation of valves in the hydraulic system connected with the pistons, to regulate the supply of hydraulic fluid to the pistons in synchronism with the operation of the printing press.

5 Claims, 2 Drawing Figures PATENTEU NOV 12 1974 3847030 SNEEI 10$ 2 APPARATUS FOR REGULATING THE DRIVE OF A PRESS OR THE LIKE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing press or the like and more particularly to a press employing a plurality of drive chains for conveying sheets, secured thereto by a plurality of gripper bars, through the press.

2. The Prior Art It is conventional in certain printing presses such as platen printing presses, in which sheet materials are printed, to provide a plurality of endless transfer chains for pulling gripper bars through the press. Each of the gripper bars is adapted to grip the forward edge of a sheet and pull the sheet through the press, stopping momentarily to enable the sheets to be successively indexed and printed. A further stopping for indexing also occurs prior to cutting the sheets.

Conventionally, springs are employed to maintain tension on the drive chains. The springs are compressed in order to slacken the chains when a sheet is held in fixed position either just prior to initial gripping by the gripping bar, or just prior to printing, cutting or the like. Such a system is disclosed in Swiss Patent No. 463,938. Alternatively, the gripper bars may be fastened to the drive chains by means of couplings which are effective to momentarily disconnect the gripper bars from the chains when the gripper bar is to be indexed. This is described in Swiss Patent No. 466,690.

Whichever of the prior art processes is employed, it is subject to one or more important disadvantages. When the chains become elongated due to the wear of the gripper bar, or inertial stress, the springs slacken and the force they exert on the chains diminishes and is often no longer sufficient to maintain an adequate chain tension. Furthermore in printing presses where the chains are slackened by compressing the springs, a relatively great effort is required to compress the springs, and the necessary force is not constant but increases with the compression of the springs. Insufficient tension on the drive chains results in excessive operating noise, due to the hammering of the chains against their guiding devices.

Moreover, with the apparatus of the prior art, accurate and frequent spring adjustment is required in order to minimize the aforesaid difficulties. Such adjustment, however, is inconvenient to perform because of the difficulty of access to the springs. The adjustment of the springs is, in any event, simply a compromise and does not attain the optimum operating characteristics.

SUMMARY OF THE PRESENT INVENTION Accordingly, it is a principal object of the present invention to provide a simple and efficient means, which is not subject to the foregoing disadvantages.

Another object of the present invention is to provide a drive mechanism for a printing press which does not employ springs for controlling the tension of the drive chains.

These and other objects and advantages of the present invention will become manifest upon an examination of the following description and the accompanying drawings.

In one embodiment of the present invention a pair of hydraulic pistons are provided for tensioning the drive chains, and a device is provided for supplying a quantity of hydraulic fluid to a cylinder housing such piston, so that a constant tension is applied to the chains irrespective of the length thereof or whether a portion of the chains are stopped for indexing.

BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made to the accompanying drawings in which:

FIG. I is a perspective view of a portion of a printing press incorporating an illustrative embodiment of the present invention; and

FIG. 2 is a perspective view of a portion of a printing press incorporating an alternative embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, there is shown spaced parallel upright frame plates 3 and 4 which support the drive chain assembly, including a pair of endless chains 1 and 2. No indexing, printing or cutting apparatus is shown in FIG. 1, but it is understood that conventional apparatus is associated with the drive chains 1 and 2 for accomplishing those functions. A plurality of gripper bars 5 have their ends interconnected to the chains 1 and 2, respectively, and the gripper bars are supported by the chains and pulled by the chains in the direction of the arrow A. Preferably, the gripper bars 5 are removably secured to the chains 1 and 2 by means, for example, such as described in Swiss Patent No. 466,690.

The chain 1 passes around a sprocket 6, mounted on a shaft 8, and the chain 2 passes around a sprocket 7, also mounted on the shaft 8. The ends of the shaft 8 are journalled in a pair of the bearings 9 and 10, which are adjustably supported by frame plates 3 and 4 by means not shown. A pair of hydraulic cylinders 11 and 12 are each provided with a piston for urging the bearings 9 and 10 leftwardly as seen in FIG. 1. Movement of the pistons within the cylinders 11 and 12 effects a movement of the bearings 9 and 10 in a direction aligned with the direction of the arrow A, serving to place the chains 1 and 2 under a tension proportional to the hydraulic pressure. The interiors of the cylinders 11 and 12 are connected via lines 13a and 13b with the outlet of a check valve 14, the inlet of which is connected over a line 13 to the outlet of a pump 17. The inlet of the pump 17 is connected with a reservoir 18, which serves as a source of fluid for the pump. A pressure gauge 15 indicates the pressure of the hydraulic fluid in the line 13. A pressure reducer 16, connected between the outlet of the pump 17 and the reservoir 18, is provided for maintaining a constant pressure of fluid on the line 13. Fluid drawn by the pump 17 from the reservoir 18 circulates through the pressure reducer l6 and'back to the reservoir, maintaining a ready source of pressurized fluid at a constant pressure on the line 13. Preferably the pressure reducer 16 is manually adjustable so that the pressure in the line 13 may be selected to be any desired value. Each of the lines 13a and 13b is provided with a drain cock, l9 and 20 respectively, by which the air trapped in the hydraulic lines may be bled out of the system.

When the printing press is initially energized, the pump 17, which is also preferably used for lubricating the various moving parts of the machine, delivers oil under pressure into the line 13, thus compensating for any losses of fluid from the cylinders 11 and 12 which may have occurred during the rest period, and forcing the pistons within the cylinders 11 and 12 leftwardly to place the chains 1 and 2 under tension. The tension in the chains 1 and 2 is directly related to the pressure on the line 13, irrespective of the length of the chains. In this way, the tension on the chains is maintained at a constant value, proportional to the pressure of the fluid in the line 13.

By means of the check valve 14 fluid flows leftwardly in the line 13, toward the cylinders 11 and 12, much more easily than rightwardly. Accordingly, when an extra load is applied to the chains, the chains are not permitted to slip backwardly because of the incompressibility of the oil within the cylinders 11 and 12, and the check valve 14. Some leakage does occur, however, rightwardly through the check valve 14, so that a steady state condition is reached in which the tension on the chains is brought to the desired value, even with increased loads that are applied to the chains. This steady state condition is not reached instantaneously, but is achieved after a comparatively short period of time.

With increased printing speeds, the tension of the chains 1 and 2 can be increased by manipulation of the pressure reducer 16, to accommodate the increased loads on the chain and to avoid hammering of the chains against their guiding devices. When the pressure is reduced in the line 13, by controlling the pressure reducer 16, a slow leakage of fluid rightwardly through the check valve 14 brings the pressure within the cylinders 11 and 12 to the desired value.

If a more rapid flow of fluid rightwardly through the lines 13a and 13b is desired, to arrive at the steady state condition more rapidly, the present invention contemplates connecting a valve in parallel with the check valve 14, such valve being controlled to open when the pressure in the line 13 falls. The valve may be controlled by electromagnetic means, and opened by an electrical signal generated in response to a fall in pressure.

In FIG. 2 an alternative embodiment of the present invention is illustrated, in which reference numerals which identify parts which are similar to those in the embodiment of FIG. 1 are primed. The chains 1 and 2' having gripper bars 5' surround the sprockets 6 and Two identical hydraulic devices 24 are connected in the branches 13a and 13b, and each includes a check valve 25 and another valve 26 connected in parallel with the check valve 25. The valves 26 are operated by cams 22 supported for rotation with a cam shaft 21. The cams 22 cooperate with operating levers 23 of the valves 26 to open and close these valves at prescribed times during each rotation of the shaft 21. Rotation of the shaft 21 is synchronized with the movement of the 4 gripper bars 5'. This is accomplished readily by driving the cam shaft 21 with the same drive unit employed for driving the chains 1' and 2'.

When the printing press is initially energized, the pump 17' delivers pressurized oil to the line 13. The valves 26 are in their closed condition, and oil is passed to the cylinders 11' and 12'. through the check valves 25, in the manner which has been described with reference to FIG. 1.

During operation of the press the movement of the gripper bars 5 is occassionally stopped, so that a sheet may be gripped by one of the gripper bars or so that a sheet may be indexed prior to printing, cutting, or the like. When the gripper bars are stopped, the chains 1 and 2' are also rendered stationary at the places where they are connected to the gripper bars 5. The continued drive of the chain causes the sprockets 6' and 7' to be urged rightwardly, forcing the respective pistons of the cylinders 11' and 12' rightwardly with the force A F. At that same moment the earns 22 bring a notched portion of their surfaces into alignment with the operating levers 23 to open the valve 26, thereby permitting fluid to flow rightwardly from the cylinders 11' and 12' through the branches 13a and 13b. In this manner the tension on the chain is maintained to a constant value, even while a portion of the chain is maintained at a stationary position during indexing of one of the gripper bars 5' At the time that motion of the gripper bar 5 is resumed, the valves 26 are again closed by action of the earns 22, and fluid is again supplied to the cylinders 11' and 12' through the check valves 25. The apparatus of FIG. 2 therefore synchronizes the application of hy draulic fluid to the cylinders 11 and 12 with the operation of the printing press. Since the cam shaft is driven by the same drive as the press, increased operating speeds of the press are accompanied by increased rotational speeds of the cam shaft 21, so that synchronization is maintained at any speed of operation of the press.

Although the present invention has been described in terms of a hydraulic system, it will be appreciated that a pneumatic system may be employed instead.

What is claimed is:

1. In a platen press having a transfer chain for intermittently driving a plurality of gripper bars, means for maintaining the chain under tension comprising a source of pressurized fluid, a cylinder connected with said source, a piston slidable within said cylinder and connected with said chain to apply a force to said chain, whereby the tension of said chain isproportional to the pressure of said fluid, means for maintaining the pressure of said fluid at a predetermined level, whereby a constant minimum tension is applied to said chain, and a check valve interconnected in the line between said source and said cylinder for preventing the rapid movement of said piston in response to a temporary increase in the tension of said chain.

2. Apparatus according to claim 1 including a reservoir, a pump coupled with said reservoir for pressurizing said fluid, and a pressure reducer interconnected between said pump and said cylinder to maintain a predetermined fluid pressure at said cylinder.

3. Apparatus according to claim 1 including a second valve connected in the circuit between said source and said cylinder, and means for controlling the operation of said valve in synchronism with the movement of said gripper bars.

6 eration of said press, and a cam mounted on said cam shaft, said cam having a notch for cooperating with the operating member of said second valve to open said valve in synchronism with the operation of said press- 

1. In a platen press having a transfer chain for intermittently driving a plurality of gripper bars, means for maintaining the chain under tension comprising a source of pressurized fluid, a cylinder connected with said source, a piston slidable within said cylinder and connected with said chain to apply a force to said chain, whereby the tension of said chain is proportional to the pressure of said fluid, means for maintaining the pressure of said fluid at a predetermined level, whereby a constant minimum tension is applied to said chain, and a check valve interconnected in the line between said source and said cylinder for preventing the rapid movement of said piston in response to a temporary increase in the tension of said chain.
 2. Apparatus according to claim 1 including a reservoir, a pump coupled with said reservoir for pressurizing said fluid, and a pressure reducer interconnected between said pump and said cylinder to maintain a predetermined fluid pressure at said cylinder.
 3. Apparatus according to claim 1 including a second valve connected in the circuit between said source and said cylinder, and means for controlling the operation of said valve in synchronism with the movement of said gripper bars.
 4. Apparatus according to claim 3 wherein said second valve is interconnected in parallel with said check valve and is operated in synchronism with the operation of said press.
 5. Apparatus according to claim 4 including a cam shaft adapted for rotation in synchronism with the operation of said press, and a cam mounted on said cam shaft, said cam having a notch for cooperating with the operating member of said second valve to open said valve in synchronism with the operation of said press. 